Detailed structure of the shallow part of the Kakuda-Yahiko fault group revealed by high-resolution S-wave reflection survey and seismic cone penetration tests

Abstract:We conducted a high-resolution S-wave reflection survey using the Land Streamer across a buried part of the Kakuda-Yahiko fault group extending N-S along the western edge of the Niigata Plain, central Japan. We also carried out the seismic cone penetration tests (CPT) to clarify Vs profiles of the near surface. The reflection profile clearly delineates a detailed structure of the surficial layers to a depth of less than 80m. Especially a buried sand dune, the eastward from about 2 m at the northwestern end to 15 m at the middle of the survey line, is evidently reconstructed. By means of the seismic CPT data, we successfully determined the depth of the dune surface, which was difficult to estimate from the reflection survey data acquired on the pavement road. The survey results profile a deformed structure beneath the sand dune, which is believed to have been formed by active faulting.